Space diversity receiver, operation controll method thereof, and program

ABSTRACT

For combining two received signals (# 1, #2 ) from different reception routes, a control process for maximizing the level of a combined signal (maximum level combining process), a control process for combining the signals in phase with each other (in-phase combining process), a control process for minimizing a waveform distortion of the combined signal (minimum amplitude deviation type combining process), and a control process for performing both the minimum amplitude deviation type combining process and the maximum level combining process are alternatively switched by an EPS (endless phase shifter) control circuit ( 8 ) depending on a level detector output ( 101 ) and a waveform distortion detector output ( 102 ). These control processes are performed by controlling the EPS ( 1 ) to control the phase of the received signal (# 2 ). With this arrangement, even in a region where the level remains substantially unchanged by phase rotation of the received signals, stable phase control can be achieved for increased system stability.

TECHNICAL FIELD

The present invention relates to a space diversity receiver, and amethod and a program for controlling operation of such a space diversityreceiver, and more particularly to a space diversity receiver forcombining received signals from a plurality of reception routes whichare distorted due to the effect of transmission paths in a wirelesszone, and a method and a program for controlling operation of such aspace diversity receiver.

BACKGROUND ART

Heretofore, diversity receivers of the type described are used tosuppress waveform distortions due to fading in transmission paths forproviding a good communication environment in microwave digital radiocommunication systems. One of such diversity receivers is a spacediversity receiver for receiving radio signals with a plurality ofreception antennas that are spaced at sufficient distances from eachother and combining a plurality of minimally correlated received signalsfrom the reception antennas for thereby reducing reception distortions.

There have been proposed various processes of combining a plurality ofreceived signals in such space diversity reception. Particularly, threeof those proposed combining processes, i.e., “in-phase combiningprocess”, “minimum amplitude deviation type combining process”, and“maximum level combining process” are mainly used in the art. The“in-phase combining process” combines received signals from a pluralityof reception routes such that the received signals are in phase witheach other, and is disclosed in Japanese laid-open patent publicationNo. 8-274695.

The “minimum amplitude deviation type combining process” detects a notchof a combined received signal and combines received signals so as tominimize an in-band amplitude deviation of the combined received signaldepending on the detected notch, is disclosed in Japanese laid-openpatent publications Nos. 59-230333 and 7-38536.

The “maximum level combining process” combines received signals suchthat the combined level thereof will be maximum. According to either oneof the above three combining processes, at least one of the receivedsignals is rotated in phase by an endless phase shifter for signalcombination. The above three combining processes have both advantagesand disadvantages, and are often used in combination. In particular, itis the general practice to use the “minimum amplitude deviation typecombining process” and the “maximum level combining process” incombination with each other.

A conventional diversity receiver based on a combination of the “minimumamplitude deviation type combining process” and the “maximum levelcombining process” will be described below. FIG. 1 of the accompanyingdrawings shows such a conventional diversity receiver. In FIG. 1,received signals #1, #2 are signals that have been received byrespective diversity antennas (not shown) and have their frequenciesconverted into an intermediate frequency range. EPS (Endless PhaseShifter) 1 is supplied with received signal #2 and an output controlsignal from EPS control circuit 8, and rotates the phase of receivedsignal #2 through unit steps (degrees) in either direction based on theoutput control signal, and outputs received signal #2 which has beenrotated in phase.

Combiner 2 is supplied with the output signal from EPS 1 and receivedsignal #1, combines these signals, and outputs the combined signal.Level detector 4 is supplied with the combined signal from combiner 2,detects the signal level of the combined signal, and outputs thedetected signal level. DEM (Demodulator) 6 is supplied with the combinedsignal from combiner 2, determines and outputs the sign of the combinedsignal.

Notch detector 7 is supplied with the combined signal from combiner 2,detects and outputs the depth (distortion) of a notch thereof. EPScontrol circuit 8 is supplied with the output signal from notch detector7 and the output signal from level detector 4, generates an optimumcontrol signal from the supplied signals, and outputs the control signalto EPS 1.

Operation of the conventional diversity receiver shown in FIG. 1 will bedescribed below. FIG. 2 of the accompanying drawings illustrates how toswitch between the combining processes. The horizontal axis of FIG. 2represents the depth of the notch (=the distortion of the waveform), andthe vertical axis the combined signal level. The depth of the notch andthe combined signal level are greater in the respective directionsindicated by the arrows. In FIG. 2, the “maximum level combiningprocess” is performed, i.e., the combined signal level is maximized(level improved), in region A. Specifically, EPS control circuit 8monitors only the output signal of level detector 4 and applies anoutput control signal to EPS 1 to rotate the phase of received signal #2in order to keep the combined signal level maximum.

In region B shown in FIG. 2, the “minimum amplitude deviation typecombining process” is performed, i.e., the in-band deviation of thecombined signal is minimized (distortion improved). Specifically, EPScontrol circuit 8 monitors the output signal of notch detector 7 andapplies an output control signal to EPS 1 to rotate the phase ofreceived signal #2 in order to minimize the distortion of the waveform.More specifically, notch detector 7 detects levels at a plurality offrequencies in the spectrum of the received signal to detect themagnitude of a change in the amplitude vs. frequency characteristics inthe band of the received signal, and EPS control circuit 8 controls EPS1 to minimize the in-band amplitude vs. frequency deviation.

If it is judged that the combined signal level is high (higher than “b”in FIG. 2) and the distortion is small (smaller than “a” in FIG. 2),then the level improving process is performed. In the distortionimproving process, since the in-band deviation is minimized depending onthe magnitude of the notch, as described above, main components of thereceived signals often tend to be combined at angles close to oppositephases, and the amplitude of the combined signal becomes low in levelthough it is flat. If the distortion is small, then because a reductionin the signal level poses a greater problem as to an error rate than thedistortion, region B is not used, but region A is used in preference fora S/N (signal level to noise level) ratio.

If only the distortion becomes greater (greater than “a” in FIG. 2),then control goes to the distortion improving process. If the distortionis large as in region B and the distortion has a greater effect on theerror rate than the level, then the distortion improving process isperformed as a sufficient distortion improving capability is expected,but the level is lowered. If the level becomes lower than “b” in FIG. 2at this time, then control goes to the level improving process becausethe level reduction poses a serious problem though some distortion mayremain unremoved (some distortion can be equalized by DFE (DecisionFeedback Equalizer) if DFE is provided at a subsequent stage).

The problem of the conventional arrangement is that the phase controlbased on the EPS is liable to be unstable if the level improving processis performed while the distortion is small and the level is high. Thisis because the level for use in the control signal is usually detectedby a diode and it is highly difficult to detect slight level changeswith the diode. The unstable phase control is responsible for a largereduction in the system stability.

DISCLOSURE OF INVENTION

It is a major object of the present invention to provide a spacediversity receiver which is capable of suppressing a reduction in systemstability to keep good reception quality, and a method and a program forcontrolling operation of such a space diversity receiver.

According to the present invention, there is provided a space diversityreceiver including phase shifting means for shifting the phase of areceived signal from a first reception route, level detecting means fordetecting the level of a combined signal which comprises an output fromthe phase shifting means and a received signal from a second receptionroute, distortion detecting means for detecting a waveform distortion ofthe combined signal, and control means for controlling the phaseshifting means depending on an output from the level detecting means andan output from the distortion detecting means, characterized in that thecontrol means switches alternatively between a control process formaximizing the level of the combined signal (maximum level combiningprocess), a control process for combining the signals in phase with eachother (in-phase combining process), and a control process for minimizingthe waveform distortion (minimum amplitude deviation type combiningprocess) depending on the output from the level detecting means and theoutput from the distortion detecting means.

The control means may switch alternatively between the maximum levelcombining process, the in-phase combining process, the minimum amplitudedeviation type combining process, and a control process which performsboth the minimum amplitude deviation type combining process and themaximum level combining process, depending on the output from the leveldetecting means and the output from the distortion detecting means. Thecontrol means may perform the maximum level combining process if theoutput from the level detecting means is smaller than a predeterminedvalue.

The control means may perform the minimum amplitude deviation typecombining process if the output from the level detecting means isgreater than the predetermined value and the output from the distortiondetecting means is greater than a first threshold “b”. The control meansmay perform the control process which performs both the minimumamplitude deviation type combining process and the maximum levelcombining process if the output from the level detecting means isgreater than the predetermined value, the output from the distortiondetecting means is smaller than the first threshold “b” and greater thana second threshold “a” (“a”<“b”).

The control means may perform the in-phase combining process if theoutput from the level detecting means is greater than the predeterminedvalue and the output from the distortion detecting means is smaller thanthe second threshold “a”. The space diversity receiver may furthercomprise phase difference detecting means for detecting a phasedifference between the output from the phase shifting means and thereceived signal from the second reception route, wherein the controlmeans controls the phase shifting means depending on the phasedifference when the control means performs the in-phase combiningprocess.

According to the present invention, there is also provided a method ofcontrolling operation of a space diversity receiver including phaseshifting means for shifting the phase of a received signal from a firstreception route, level detecting means for detecting the level of acombined signal which comprises an output from the phase shifting meansand a received signal from a second reception route, and distortiondetecting means for detecting a waveform distortion of the combinedsignal, wherein the phase shifting means is controlled depending on anoutput from the level detecting means and an output from the distortiondetecting means, characterized by the control step of switchingalternatively between a control process for maximizing the level of thecombined signal (maximum level combining process), a control process forcombining the signals in phase with each other (in-phase combiningprocess), and a control process for minimizing the waveform distortion(minimum amplitude deviation type combining process) depending on theoutput from the level detecting means and the output from the distortiondetecting means.

The control step may switch alternatively between the maximum levelcombining process, the in-phase combining process, the minimum amplitudedeviation type combining process, and a control process which performsboth the minimum amplitude deviation type combining process and themaximum level combining process, depending on the output from the leveldetecting means and the output from the distortion detecting means. Thecontrol step may perform the maximum level combining process if theoutput from the level detecting means is smaller than a predeterminedvalue.

The control step may perform the minimum amplitude deviation typecombining process if the output from the level detecting means isgreater than the predetermined value and the output from the distortiondetecting means is greater than a first threshold “b”. The control stepmay perform the control process which performs both the minimumamplitude deviation type combining process and the maximum levelcombining process if the output from the level detecting means isgreater than the predetermined value, the output from the distortiondetecting means is smaller than the first threshold “b” and greater thana second threshold “a” (“a”<“b”).

The control step may perform the in-phase combining process if theoutput from the level detecting means is greater than the predeterminedvalue and the output from the distortion detecting means is smaller thanthe second threshold “a”. The method of controlling operation mayfurther comprise the step of detecting a phase difference between theoutput from the phase shifting means and the received signal from thesecond reception route, wherein the control step controls the phaseshifting means depending on the phase difference when the control stepperforms the in-phase combining process.

According to the present invention, there is further provided a programfor enabling a computer to perform a method of controlling operation ofa space diversity receiver including phase shifting means for shiftingthe phase of a received signal from a first reception route, leveldetecting means for detecting the level of a combined signal whichcomprises an output from the phase shifting means and a received signalfrom a second reception route, and distortion detecting means fordetecting a waveform distortion of the combined signal, wherein thephase shifting means is controlled depending on an output from the leveldetecting means and an output from the distortion detecting means,characterized by the control step of switching alternatively between acontrol process for maximizing the level of the combined signal (maximumlevel combining process), a control process for combining the signals inphase with each other (in-phase combining process), and a controlprocess for minimizing the waveform distortion (minimum amplitudedeviation type combining process) depending on the output from the leveldetecting means and the output from the distortion detecting means.

Operation of the present invention will be described below. According tothe present invention, the combining processes are switched depending onthe detected distortion of the combined signal and the detected level ofthe combined signal. Specifically, the control process for maximizingthe level of the combined signal (maximum level combining process), thecontrol process for combining the signals in phase with each other(in-phase combining process), the control process for minimizing thewaveform distortion (minimum amplitude deviation type combiningprocess), and in addition, the control process which performs both theminimum amplitude deviation type combining process and the maximum levelcombining process, are alternatively switched depending on the outputfrom the level detecting means and the output from the distortiondetecting means. With this arrangement, even in a region where the levelremains substantially unchanged by phase rotation of the receivedsignals, stable phase control can be achieved for increased systemstability.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of a conventional arrangement;

FIG. 2 is a diagram showing a combination control map in theconventional arrangement shown in FIG. 1;

FIG. 3 is a block diagram of an arrangement according to an embodimentof the present invention;

FIG. 4 is a diagram showing a combination control map in the arrangementaccording to the embodiment of the present invention; and

FIG. 5 is a flowchart of an operation sequence of an EPS control circuitshown in FIG. 3.

BEST MODE FOR CARRYING OUT THE INVENTION

An embodiment of the present invention will be described below withreference to the drawings. FIG. 3 is a block diagram of an arrangementaccording to the embodiment of the present invention. Those parts shownin FIG. 3 which are equivalent to those shown in FIG. 1 are denoted byidentical reference characters. According to the present invention,components described below are added to the arrangement shown in FIG. 1.Those components include AGC (Automatic Gain Control) circuit 3 foramplifying received signal #1 to a predetermined level, AGC signal 5 foramplifying the output signal of EPS 1 to a predetermined level, andphase detector 9 for being supplied with output signals from AGCcircuits 3, 5 to detect a phase difference therebetween.

EPS control circuit 8 is supplied with detected phase output S3 fromphase detector 9, level detector output 101, and notch detector output102, and controls EPS 1 based on the supplied three signals. Otherstructural details of the arrangement shown in FIG. 3 are identical tothose shown in FIG. 1, and will not be described below.

FIG. 4 shows a control map illustrative of a process of switchingbetween combination control algorithms. The horizontal axis of FIG. 4represents the depth of the notch (=the distortion of the waveform), andthe vertical axis the combined signal level. The depth of the notch andthe combined signal level are greater in the respective directionsindicated by the arrows. In FIG. 4, a control process for improving thelevel is performed in region A, a control process for improving thedistortion is performed in region B, a control process for improvingboth the distortion and the level is performed in region C, and anin-phase combining process is performed in region D.

Operation of the embodiment of the present invention will be describedbelow with reference to FIGS. 3 and 4. According to the presentinvention, the “in-phase combining process” is added to the combiningprocesses that are performed according to the conventional arrangement.The “in-phase combining process” is a process of controlling the signalsfrom respective transmission routes in phase with output voltage S3 fromphase detector 9 and combining the signals in phase. In order to performthe “in-phase combining process”, the arrangement according to theembodiment of the present invention additionally has AGC circuits 3, 5and phase detector 9 for detecting the phases of the signals from therespective transmission routes, in addition to the conventionalarrangement.

Generally, the phase detection performed by a phase detector has ahigher detection sensitivity in the vicinity of an in-phase combiningangle than the level detection performed by a diode level detector. If awaveform distortion is small and a combined signal level is high, it ispossible to perform appropriate phase shift control for higher systemstability by carrying out the in-phase combining process (region D)rather than the level improving process (region A). However, thein-phase combining process is not effective to suppress interferencewaves that are responsible for waveform distortions, as is the case withthe level improving process.

As described above, the region where the in-phase combining process isperformed is referred to as region D as shown in FIG. 4.

Another difference between the embodiment of the present invention andthe conventional arrangement is that region C is defined between regionD and region B. In region C, the values of the distortion and the levelbefore and after the phase is rotated by EPS 8 are compared to determinea direction in which to rotate the phase. Specifically, after the phaseof received signal #2 is rotated by EPS 8 through a certain angle in acertain direction, the output signal from level detector 4 and theoutput signals from notch detector 7 before and after the phase isfurther rotated are referred to. The phase is rotated in the samedirection only if improvements in both the level and the distortion arerecognized, and is reversed otherwise.

The reasons why region C is included will be described below. Forcontrol to shift from region B to region D, the condition of a smallerdistortion has to be satisfied. However, the receiver itself is unableto determine whether the distortion became smaller because the status ofthe transmission paths had been improved or because of the distortionimproving effect in region B. Therefore, control tends to shift toregion D because of the latter phenomenon. Actually, however, sincewaveform distortions are present due to the transmission paths, waveformdistortions are developed again by a phase rotation from an optimumpoint in region B to an optimum point in region D, causing control toshift to region B, resulting in a type of oscillatory control action. Tosolve this problem, the distortion improving process is performed whileobserving the level. Inasmuch as the level increases as the status ofthe transmission paths is improved, it is possible to determine whetherthe distortion becomes smaller because the status of the transmissionpaths is improved or because of the distortion improving effect inregion B, so that the above oscillatory control action can be avoided.

For control to shift from region D to region B, the phase shiftingcontrol performed by EPS 8 poses a problem. As described above, theposition of a phase close to an opposite phase is stable in region Bdepending on the distortion. Since the position of a phase tends tobecome closer to an opposite phase as the distortion is larger, ifcontrol shifts to region B from a state where the distortion is large toa certain extent, then a phase difference of nearly 180 degrees isdeveloped with region A where the in-phase combining process is carriedout. As a result, the phase shifting control cannot catch up, tending tocause a circuit disconnection in the worst case. Region C is inserted toallow control to shift to the distortion improving process when thedistortion is relatively small (at “a” in FIG. 4).

FIG. 5 shows an operation sequence of EPS control circuit 8 shown inFIG. 3. First, if level detector output 101 is equal to or lower thanpredetermined value “c” in FIG. 4, then the maximum level combiningprocess (region A shown in FIG. 4) is performed (steps 10, 20). That is,the maximum level combining process is performed to maximize leveldetector output 101.

If the condition of step 10 is not satisfied, then control goes to step30 which compares notch detector output 102 with first threshold “b”. Ifnotch detector output 102 is greater than first threshold “b”, theminimum amplitude deviation type combining process (region B in FIG. 4)is performed (step 40). That is, the minimum amplitude deviation typecombining process is performed to minimize the in-band deviation of thecombined signal (distortion improved).

If the condition of step 30 is not satisfied, then control goes to step50 which compares notch detector output 102 with second threshold “a”.If notch detector output 102 is greater than second threshold “a” andsmaller than first threshold “b”, then the combining process (region Cin FIG. 4) for performing both the minimum amplitude deviation typecombining process and the maximum level combining process is performed(step 60). Otherwise, the in-phase combining process (region D in FIG.4) is performed (step 70). Specifically, EPS 1 is controlled in orderfor detected phase output S3 to represent phase difference “0”. It isapparent that the flowchart shown in FIG. 3 is a looped sequence(program) for repeatedly carrying out the steps between “START” and“END”.

The switching control process shown in FIGS. 4 and 5 may be performed byprestoring the operation sequence shown in FIG. 4 as a program in arecording medium and having a computer (CPU) read and executing thestored program from the recording medium.

The arrangement according to the embodiment of the present invention isadvantageous in that the S/N ratio of a combined signal at the timereceived signals are of a low distortion and a high level can stably bemaximized without the need for any special circuits to be added. Thereason for such an advantage is that the in-phase combining process iscarried out instead of the conventional level improving process forthereby performing phase detection of high accuracy rather than leveldetection of low accuracy. Thus, even in a region where the levelremains substantially unchanged by phase rotation, stable phase controlcan be achieved for increased system stability.

1. A space diversity receiver comprising: phase shifting means forshifting the phase of a received signal from a first reception route;level detecting means for detecting the level of a combined signal whichcomprises an output from said phase shifting means and a received signalfrom a second reception route; distortion detecting means for detectinga waveform distortion of said combined signal; and control means forcontrolling said phase shifting means depending on an output from saidlevel detecting means and an output from said distortion detectingmeans, wherein said control means switches alternatively between acontrol process for maximizing the level of said combined signal(maximum level combining process), a control process for combining thesignals in phase with each other (in-phase combining process), and acontrol process for minimizing said waveform distortion (minimumamplitude deviation type combining process) depending on the output fromsaid level detecting means and the output from said distortion detectingmeans, and performs said maximum level combining process if said outputfrom said level detecting means is smaller than a predetermined value,wherein said control means performs said minimum amplitude deviationtype combining process if said output from said level detecting means isgreater than said predetermined value and said output from saiddistortion detecting means is greater than a first threshold “b”, andwherein said control means performs a control process which performsboth said minimum amplitude deviation type combining process and saidmaximum level combining process if said output from said level detectingmeans is greater than said predetermined value, said output from saiddistortion detecting means is smaller than said first threshold “b” andgreater than a second threshold “a”, wherein “a” is less than “b”.
 2. Aspace diversity receiver according to claim 1, wherein said controlmeans performs said in-phase combining process if said output from saidlevel detecting means is greater than said predetermined value and saidoutput from said distortion detecting means is smaller than said secondthreshold “a ”.
 3. A space diversity receiver according to claim 2,further comprising: phase difference detecting means for detecting aphase difference between the output from said phase shifting means andthe received signal from said second reception route; wherein saidcontrol means controls said phase shifting means depending on said phasedifference when said control means performs said in-phase combiningprocess.
 4. A method of controlling operation of a space diversityreceiver including phase shifting means for shifting the phase of areceived signal from a first reception route, level detecting means fordetecting the level of a combined signal which comprises an output fromsaid phase shifting means and a received signal from a second receptionroute, and distortion detecting means for detecting a waveformdistortion of said combined signal, wherein said phase shifting means iscontrolled depending on an output from said level detecting means and anoutput from said distortion detecting means, the control methodcomprising: switching alternatively between a control process formaximizing the level of said combined signal (maximum level combiningprocess), a control process for combining the signals in phase with eachother (in-phase combining process), and a control process for minimizingsaid waveform distortion (minimum amplitude deviation type combiningprocess) depending on the output from said level detecting means and theoutput from said distortion detecting means, and performing said maximumlevel combining process if said output from said level detecting meansis smaller than a predetermined value, wherein said control stepperforms said minimum amplitude deviation type combining process if saidoutput from said level detecting means is greater than saidpredetermined value and said output from said distortion detecting meansis greater than a first threshold “b”, and wherein said control stepperforms said control process which performs both said minimum amplitudedeviation type combining process and said maximum level combiningprocess if said output from said level detecting means is greater thansaid predetermined value, said output from said distortion detectingmeans is smaller than said first threshold “b” and greater than a secondthreshold “a”, wherein “a” is less than “b”.
 5. A method of controllingoperation according to claim 4, wherein said control step performs saidin-phase combining process if said output from said level detectingmeans is greater than said predetermined value and said output from saiddistortion detecting means is smaller than said second threshold “a”. 6.A method of controlling operation according to claim 5, furthercomprising the step of: detecting a phase difference between the outputfrom said phase shifting means and the received signal from said secondreception route; wherein said control step controls said phase shiftingmeans depending on said phase difference when said control step performssaid in-phase combining process.
 7. A program for enabling a computer toperform a method of controlling operation of a space diversity receiverincluding phase shifting means for shifting the phase of a receivedsignal from a first reception route, level detecting means for detectingthe level of a combined signal which comprises an output from said phaseshifting means and a received signal from a second reception route, anddistortion detecting means for detecting a waveform distortion of saidcombined signal, wherein said phase shifting means is controlleddepending on an output from said level detecting means and an outputfrom said distortion detecting means, comprising the control step of:switching alternatively between a control process for maximizing thelevel of said combined signal (maximum level combining process), acontrol process for combining the signals in phase with each other(in-phase combining process), and a control process for minimizing saidwaveform distortion (minimum amplitude deviation type combining process)depending on the output from said level detecting means and the outputfrom said distortion detecting means, and performs said maximum levelcombining process if said output from said level detecting means issmaller than a predetermined value, wherein said control step performssaid minimum amplitude deviation type combining process if said outputfrom said level detecting means is greater than said predetermined valueand said output from said distortion detecting means is greater than afirst threshold “b”, and wherein said control step performs said controlprocess which performs both said minimum amplitude deviation typecombining process and said maximum level combining process if saidoutput from said level detecting means is greater than saidpredetermined value, said output from said distortion detecting means issmaller than said first threshold “b” and greater than a secondthreshold “a” wherein “a” is less than “b”.
 8. A program according toclaim 7, wherein said control step performs said in-phase combiningprocess if said output from said level detecting means is greater thansaid predetermined value and said output from said distortion detectingmeans is smaller than said second threshold “a”.
 9. A program accordingto claim 8, further comprising the step of: detecting a phase differencebetween the output from said phase shifting means and the receivedsignal from said second reception route; wherein said control stepcontrols said phase shifting means depending on said phase differencewhen said control step performs said in-phase combining process.